Here is the full list of all 12 Bastion achievements worth 200 gamerscore. It takes around 8-10 hours to unlock all of the achievements on Xbox 360.
Complete the story in New Game Plus.
Complete the story, embracing the New World.
Complete the story.
Complete each trip to Who Knows Where.
Complete 100 percent of the Vigils in the Memorial.
Use the Forge to apply at least one upgrade to every weapon.
Stop the siege on the Bastion.
Get four different domesticated creatures in the Bastion.
Complete at least 50 percent of the Vigils in the Memorial.
Complete Prosper Bluff and speak with the Singer in the Bastion.
Complete the Hanging Gardens and speak with the Survivor in the Bastion.
Complete the Wharf District.